Irregular shapes under Section VIII, Div 1? 1

[hhamza]

I'm trying to create a calculation package for a pressure vessel that does not have a standard shape (i.e. not a shell, hemisphere, conical, etc.) Is there a way to perform this calculation under Division 1 rules? For instance, if I can fit a hemisphere entirely inside my part, can I design it as a hemihead knowing that my calculation is conservative? I would appreciate your reasoning either for or against using this approach.

My second question is regarding the 3000 PSI limit in U1(d). Is there any clarification about what the "additional design principles and construction practices" are for vessels rated above 3000 PSI?

Thanks,

 

[jte]

if I can fit a hemisphere entirely inside my part, can I design it as a hemihead knowing that my calculation is conservative?

hhamza- Coupling your statement above of what you believe to possibly be factual with your prior query thread794-389325 about how to calculate area of reinforcement for openings, I have a couple suggestions.

First, read the Foreword. Specifically, the fourth paragraph. I'll copy it in to here for easy reference:

The Code is not a handbook and cannot replace education, experience, and the use of engineering judgment. The phrase engineering judgement refers to technical judgments made by knowledgeable engineers experienced in the application of the Code. Engineering judgments
must be consistent with Code philosophy, and such judgments must never be used to overrule mandatory requirements or specific prohibitions of the Code.

Second, regarding your query about the 3000 psi note, I'll suggest you read ASME PCC-2 Article 5, Appendix II and III. Then re-read the fourth paragraph of the Foreword.

 

[hhamza]

I don't really understand your first point. My previous post is completely unrelated to this question (other than the fact they both deal with section viii, division 1).

 

[TGS4]

Is there a way to perform this calculation under Division 1 rules?

Yes - U-2(g).

Within the rules contained in Division 1? No. Whatever your shape is, I can guarantee that the stresses will be more than that of an equivalent hemispherical head. Therefore, your contention that such a calculation would be more conservative is incorrect. My rationale is based on strength of materials and thin-shell theory.

Is there any clarification about what the "additional design principles and construction practices" are for vessels rated above 3000 PSI?

At pressures above 3000psi, the thin-shell theory assumptions built-in to the Division 1 calculations are generally rendered invalid. Rather than trying to figure what these additional design principles and construction practices are, you be better off using Division 2. However, if your pressures exceed 10,000psi, then, as recommended by Division 2, paragraph 1.2.2.2, you would be better served by using Division 3.

 

[JStephen]

Note that a cube-shaped vessel that would fit inside a hemisphere could have far higher stresses.

Also note that in some cases, it is advantageous to change the shape to match the design methods available, even if other shapes might actually be workable.